The stereochemical requirements for biological activity in the enkephalin segment, i.e. residues 1-5 of .beta.-endorphin has recently been examined by Yamashiro et al., Int. J. Peptide Protein Res. 10, 159 (1977). Substitution of amino acids in positions 1, 4 and 5 by the corresponding D-isomers resulted in drastic decreases in biological activity for each of the three analogs. On the other hand replacement of glycine in position 2 by D-alanine gave an analog with potency comparable to that of the parent molecule. With the enkephalins this replacement greatly increases analgesic activity. In the report on the isolation of the enkephalins (Hughes et al. Nature (Lond.) 258, 258 (1975) the existence of methionine and leucine forms was noted. A parallel leucine form of .beta.-endorphin has been suggested to have been found in renal dialysis fluid of schizophrenic patients by Dr. Roberta Palmour at the Conference on Endorphins In Mental Health Research in San Juan, Puerto Rico during Dec. 11-13, 1977 after completion of the studies upon which the present application is based.